Typical of prior art epoxy resin compositions used in encapsulating semiconductor devices are epoxy resin compositions having blended therein a curing agent such as a phenol resin and an inorganic filler such as silica. These epoxy resin compositions are advantageous for encapsulating semiconductor devices. Because of their low melt viscosity and a high melt flow compared with other thermosetting resin compositions such as phenol resin compositions, these epoxy resin compositions are effective in imparting improved moisture resistance to LSI, IC and transistors while minimizing damage to fine patterns and wires thereon.
The recent trend that silicon chips are increased in size and the wiring spacing is minimized imposes a demand for approximating the coefficient of expansion of semiconductor capsulants to that of silicon chips. One approach is to increase the amount of filler blended in the epoxy resin composition to reduce the coefficient of expansion of the cured composition.
On the other hand, a more flowing encapsulant is desired to meet the demand for larger size, multiple pin packages. In general, as the amount of filler increases, the epoxy resin composition flows poorly and is inefficiently molded as often inviting voids and wire flow during molding, resulting in a cured product having poor moisture resistance. There is a need for the development of a semiconductor encapsulating epoxy resin composition having a high flow and moldability and capable of forming a cured product having a low coefficient of expansion.
For epoxy resin compositions comprising an epoxy resin, a curing agent, and an inorganic filler, some approaches are made as by adding a silicone or polybutadiene base modifier to reduce stressing or increasing the amount of inorganic filler blended to reduce the coefficient of expansion. These approaches have some drawbacks although they can reduce stressing. Increasing the amount of inorganic filler blended adversely affects the flow of the composition during molding and the moisture resistance of the cured product upon soldering after moisture absorption. It is difficult to establish a compromise among important functions for encapsulants such as low stressing, moisture resistance upon soldering after moisture absorption, and melt flow.
There is another demand for thinner semiconductor devices as typified by flat packages and SOJ packages. In mounting thin semiconductor devices on printed circuit boards, the presence of moisture in the package could invite water vapor explosion which would induce cracks in the package and gaps at the surface of the silicon chip.
Therefore, there is a need for the development of a semiconductor encapsulating epoxy resin composition exhibiting a high flow upon molding and capable of forming a cured product having low stress and improved soldering resistance, especially moisture resistance and crack resistance after moisture absorption.